The Interstellar Boundary Explorer (IBEX) mission is a NASA-funded satellite that orbits Earth and maps the boundary of our Solar System from Earthâs point of view looking outward. IBEX has completed the first all-sky maps of this boundary by detecting particles traveling inward from the boundary toward our region of the Solar System. The map appears to be oval in shape for the same reason that two-dimensional maps of spherical Earth look oval. The boundary of our Solar System is created by the interaction between charged particles from the Sun that are streaming outward, called the solar wind, and material between the stars, called the interstellar medium (ISM). The solar wind flows outward into space and carves out a protective bubble, called the heliosphere, in the ISM around our Solar System. At the boundary, the interactions between the solar wind particles and the ISM particles create energetic neutral atoms (ENAs). ENAs are particles with no charge that move very fast. Some of the ENAs happen to be traveling in just the right way so that they move inward through the Solar System toward Earth where IBEX can collect them. Using two sensors, called IBEX-Hi and IBEX-Lo, the spacecraft measures and counts these ENAs. The scientists can create maps of the boundary using this information. For each small area of the sky, IBEX has measured the number of ENAs coming from that direction. This map shows the distribution of ENAs ranging in energy from 0.6 to 1.0 keV. Red indicates the highest number of ENAs measured by the spacecraft. Yellow and green indicate lower numbers of ENAs, and blue and purple show the lowest number of ENAs.

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